This invention relates to a process and apparatus for the biological purification of phosphate-containing wastewater wherein the wastewater is treated in the presence of activated sludge, at least a portion of which is fixed on a carrier material, in at least one aerobic, an anaerobic, and optionally an anoxic zone or stage, and thereafter a substantially phosphate-free wastewater stream is discharged.
DAS No. 2,839,872 discloses a process wherein organic hydrocarbon compounds are degraded through the use of microorganisms fixed on a carrier material. In addition, nitrification and dentrification can be conducted, and phosphates are removed by chemical means from the wastewater. To effect the removal of phosphates from the wastewater, the biomass in this process is subjected in an alternating manner to aerobic and anaerobic conditions. In order to achieve this in relatively tightly packed reactors, the applicant in DAS No. 2,839,872 teaches utilizing a stationary carrier material as taught in West German patent application No. P 32 15 404.6, and effecting the alternation of the aerobic/anaerobic treatment for the phosphate elimination by means of a complicated switching of cycles.